#include <stdio.h>
#include <signal.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netdb.h>
#include <setjmp.h>
#include <errno.h>

#define PACKET_SIZE 4096
#define MAX_WAIT_TIME 5
#define MAX_NO_PACKETS 3

char sendpacket[PACKET_SIZE];
char recvpacket[PACKET_SIZE];
int sockfd, datalen = 56;
int nsend = 0, nreceived = 0;
struct sockaddr_in addr, dest_addr;
pid_t pid;
struct sockaddr_in from;
struct timeval tvrecv;

void statistics(int signo);
unsigned short cal_chksum(unsigned short *addr, int len);
int pack(int pack_no);
void send_packet(void);
void recv_packet(void);
int unpack(char *buf, int len);
void tv_sub(struct timeval *out, struct timeval *in);

void statistics(int signo)
{
    printf("\n----------PNG statistics----------\n");
    printf("%d packets transmitted, %d received,%%%d lost\n", nsend, nreceived, (nsend - nreceived) / nsend * 100);
    close(sockfd);
    exit(1);
}

//检验和算法
unsigned short cal_chksum(unsigned short *addr, int len)
{
    int nleft = len;
    int sum = 0;
    unsigned short *w = addr;
    unsigned short answer = 0;
    //把ICMP报头二进制数据以2字节为单位累加起来
    while (nleft > 1)
    {
        sum += *w++;
        nleft -= 2;
    }
    //若ICMP报为奇数个字节，会剩下最后一字节。把最后一个字节是为一个2字节数据的高字节，这个2字节数据的低字节为0，继续累加
    if (nleft == 1)
    {
        *(unsigned char *)(&answer) = *(unsigned char *)w;
        sum += answer;
    }
    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);
    answer = ~sum;
    return answer;
}

//设置ICMP报头
int pack(int pack_no)
{
    int i, packsize;
    struct icmp *icmp;
    struct timeval *tval;

    icmp = (struct icmp *)sendpacket;
    icmp->icmp_type = ICMP_ECHO;
    icmp->icmp_code = 0;
    icmp->icmp_cksum = 0;
    icmp->icmp_seq = pack_no;
    icmp->icmp_id = pid;
    packsize = 8 + datalen;
    tval = (struct timevla *)icmp->icmp_data;
    gettimeofday(tval, NULL);                                        //记录发送时间
    icmp->icmp_cksum = cal_chksum((unsigned short *)icmp, packsize); //检验算法
    return packsize;
}

//发送3个ICMP报文
void send_packet()
{
    int packetsize;
    while (nsend < MAX_NO_PACKETS)
    {
        nsend++;
        packetsize = pack(nsend); //设置ICMP报头
        if (sendto(sockfd, sendpacket, packetsize, 0, (struct sockaddr *)&dest_addr, sizeof(dest_addr)) < 0)
        {
            perror("sendto error!\n");
            continue;
        }
        sleep(1); //每隔一秒发送一个ICMP报文
    }
}

//接收所有ICMP报文
void recv_packet()
{
    int n, fromlen;
    extern int errno;

    signal(SIGALRM, statistics);
    fromlen = sizeof(from);
    while (nreceived < nsend)
    {
        alarm(MAX_NO_PACKETS);
        if ((n = recvfrom(sockfd, recvpacket, sizeof(recvpacket), 0, (struct sockaddr *)&from, &fromlen)) < 0)
        {
            if (errno == EINTR)
                continue;
            perror("recvfrom error!\n");
            continue;
        }
        gettimeofday(&tvrecv, NULL); //记录接收时间
        if (unpack(recvpacket, n) == -1)
            continue;
        nreceived++;
    }
}

//剥去ICMP报头
int unpack(char *buf, int len)
{
    int i, iphdrlen;
    struct ip *ip;
    struct icmp *icmp;
    struct timeval *tvsend;
    double rtt;

    ip = (struct ip *)buf;
    iphdrlen = ip->ip_hl << 2;                  //求IP报头长度，即IP报头的长度标志×4
    iphdrlen = (struct icmp *)(buf + iphdrlen); //越过IP报头，指向ICMP报头
    len -= iphdrlen;                            // ICMP报头及ICMP数据报的总长度
    if (len < 8)                                //小于ICMP报头长度则不合理
    {
        printf("ICMP packets\'s length is less than 8\n");
        return -1;
    }
    //确保所接收的是我所发的ICMP的回应
    if ((icmp->icmp_type == ICMP_ECHOREPLY) && (icmp->icmp_id == pid))
    {
        tvsend = (struct timeval *)icmp->icmp_data;
        tv_sub(&tvrecv, tvsend);                            //接收和发送的时间差
        rtt = tvrecv.tv_sec * 1000 + tvrecv.tv_usec / 1000; //以毫秒为单位计算 rtt
        printf("%d byte from %s:icmp_seq=%u ttl=%d rtt=%.3f ms\n", len, inet_ntoa(from.sin_addr), icmp->icmp_seq, ip->ip_ttl, rtt);
    }
    else
        return -1;
}

//主函数
int main(int argc, char *argv[])
{
    struct hostent *host;
    struct protoent *protocol;
    unsigned long inaddr = 01;
    int waittime = MAX_NO_PACKETS;
    int size = 50 * 1024;

    if (argc < 2)
    {
        printf("usage:%s hostname/IP address\n", argv[0]);
        exit(1);
    }
    if ((protocol = getprotobyname("icmp")) == NULL)
    {
        perror("getprotobyname error!\n");
        exit(1);
    }
    //生成使用ICMP的原始套接字，这种套接字只有root才能生成
    if ((sockfd = socket(AF_INET, SOCK_RAW, protocol->p_proto)) < 0)
    {
        perror("socket error");
        exit(1);
    }
    //回收root权限，设置当前用户权限
    setuid(getuid());
    //扩大套接字接收缓冲区到50KB，这样做主要为了减小接收缓冲区溢出的可能性，若无意中ping一个广播地址或多播地址，将会进来大量应答
    setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &size, sizeof(size));
    bzero(&dest_addr, sizeof(dest_addr));
    dest_addr.sin_family = AF_INET;
    //判断是主机名还是IP地址
    if ((inaddr = inet_addr(argv[1])) == INADDR_NONE)
    {
        //是主机名
        if ((host = gethostbyname(argv[1])) == NULL)
        {
            perror("gethostbyname error !\n");
            exit(1);
        }
        memcpy((char *)&dest_addr.sin_addr, host->h_addr, host->h_length);
    }
    //是IP地址
    else
        dest_addr.sin_addr.s_addr = inet_addr(argv[1]);
    pid = getpid();
    signal(SIGINT, statistics);
    printf("PING %s(%s): %d bytes data in ICMP packets.\n", argv[1], inet_ntoa(dest_addr.sin_addr), datalen);
    send_packet();
    recv_packet();
    statistics(SIGALRM);
    return 0;

    //     memcpy((char *)&dest_addr, (char *)&inaddr, host->h_length);
    // //获取main的进程id，用于设置ICMP的标识符
    // pid = getpid();
    // printf("PING %s(%s): %d bytes data in ICMP packets.\n", argv[1], inet_ntoa(dest_addr.sin_addr), datalen);
    // send_packet();       //发送所有ICMP报文
    // recv_packet();       //接收所有ICMP报文
    // statistics(SIGALRM); //进行统计
    // return 0;
}

//两个timeval结构相减
void tv_sub(struct timeval *out, struct timeval *in)
{
    if ((out->tv_usec -= in->tv_usec) < 0)
    {
        --out->tv_sec;
        out->tv_usec += 1000000;
    }
    out->tv_sec -= in->tv_sec;
}

//缺少调试信息的提示
// debuginfo-install glibc-2.17-260.el7.x86_64